Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who takes Pegasys (Peginterferon-alfa-2a). If you are concerned about side effects, discuss the risks and benefits of Pegasys (Peginterferon-alfa-2a) with your doctor.

The following side effects have been reported by at least 1% of people taking Pegasys (Peginterferon-alfa-2a). Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

• back pain
• cough
• decreased desire for sexual activities
• Diarrhea
• dry, itchy skin
• Dry Mouth
• fatigue
• flu-like symptoms (unusual tiredness, Fever, chills, muscle aches, joint pain, and Headaches)
• hair thinning
• loss of appetite
• nausea
• poor concentration
• rash
• redness, swelling, bruising, irritation, or itching at the site of the injection
• trouble sleeping
• vomiting

Although most of the side effects listed below don't happen very often, they could lead to serious problems if you do not seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

• Anemia (paleness, tiredness, shortness of breath)
• bloody diarrhea
• changes in mood (e.g., irritability, anxiety, aggression)
• dizziness
• hallucinations (seeing or hearing things that are not there)
• high blood sugar (increased thirst, hunger, weakness, drowsiness, blurred vision, weight loss)
• loss of coordination
• low blood sugar (headache, hunger, weakness, irritability, trouble concentrating)
• lower back or side pain
• lung problems (e.g., difficulty breathing, pneumonia)
• numbness or tingling or burning sensations
• persistent cough
• signs of Depression (e.g., poor concentration, changes in weight, changes in sleep, decreased interest in activities, thoughts of suicide)
• signs of infection (e.g., chills, fever, cough, sore throat, difficulty or painful urination, difficulty breathing)
• ulcers or sores in the mouth or throat
• unusual bruising or bleeding (e.g., bleeding gums, nosebleeds, blood in the urine, pinpoint-sized red spots on skin)
• vision changes (e.g., blurred vision, loss of vision)
• weakness
• worsening psoriasis

Stop taking the medication and seek immediate medical attention if any of the following occur:

• fast or irregular heartbeat (palpitations)
• severe skin rash (blistering, peeling, and spreading)
• suicidal feelings or suicide attempts
• symptoms of a Heart Attack (e.g., severe chest pain or pressure, pain in the arm or shoulder, nausea, sweating)
• symptoms of a Anaphylaxis (severe allergic reaction) (e.g., Hives; difficulty breathing; swelling of the face, mouth, throat, or tongue)
• symptoms of a Stroke (e.g., sudden and severe headache, sudden weakness or numbness in the arms or legs, sudden vision changes, sudden dizziness)
• trouble breathing

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking Pegasys (Peginterferon-alfa-2a).

180 µg/0.5 mL (prefilled syringe)
Each 0.5 mL of sterile, ready-to-use solution for subcutaneous injection contains 180 µg of peginterferon alfa-2a (expressed as the amount of interferon alfa-2a). Nonmedicinal ingredients: sodium chloride, 80 polysorbate, benzyl alcohol, sodium acetate trihydrate, acetic acid, and water for injection.

180 µg/mL (single use vial)
Each mL of sterile, ready-to-use solution for subcutaneous injection contains 180 µg of peginterferon alfa-2a (expressed as the amount of interferon alfa-2a). Nonmedicinal ingredients: sodium chloride, 80 polysorbate, benzyl alcohol, sodium acetate trihydrate, acetic acid, and water for injection.

180 µg/0.5 mL (ProClick™ Autoinjector)
Each mL of sterile, ready-to-use solution for subcutaneous injection contains 180 µg of peginterferon alfa-2a (expressed as the amount of interferon alfa-2a). Nonmedicinal ingredients: sodium chloride, 80 polysorbate, benzyl alcohol, sodium acetate trihydrate, acetic acid, and water for injection.

The ready-to-use autoinjector includes a post-injection needle shield designed to help prevent needle-stick injuries and keep the needle non-visible.

Do not use Pegasys (Peginterferon-alfa-2a) if you:

• are allergic to peginterferon alfa-2a, or any ingredients of the medication
• are allergic to any other interferon, to E. coli-derived products, or polyethylene glycol
• have autoimmune hepatitis
• have a history of other autoimmune disease
• have decompensated cirrhosis
• have HIV-HCV (human immunodeficiency virus and hepatitis C virus) with cirrhosis and a baseline Child-Pugh score greater than or equal to 6
• have a history of a severe psychiatric condition
• have an uncorrected Thyroid condition
• are breast-feeding

Do not give Pegasys (Peginterferon-alfa-2a) to children less than 6 months of age.

There may be an interaction between peginterferon alfa-2a and any of the following:

• Aldesleukin
• BCG
• Chinese herbal medicine (sho-saiko-to or Xiao-Chai-Hu)
• Clozapine
• Deferiprone
• dipyrone
• Methadone
• ribavirin
• telbivudine
• theophyllines (Aminophylline, Oxtriphylline, Theophylline)
• Tizanidine
• zidovudine

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

• stop taking one of the medications,
• change one of the medications to another,
• change how you are taking one or both of the medications, or
• leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with Pegasys (Peginterferon-alfa-2a). Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the Nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.

Before you begin using a medication, be sure to inform your doctor of any medical conditions or Allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use Pegasys (Peginterferon-alfa-2a).

Allergic reactions: In rare cases, Pegasys (Peginterferon-alfa-2a) may cause severe allergic reactions. If you notice hives, swelling of the face or throat, or difficulty breathing, stop using Pegasys (Peginterferon-alfa-2a) and get medical help immediately.

Autoimmune conditions: Pegasys (Peginterferon-alfa-2a) may cause or worsen autoimmune conditions including myositis, hepatitis, immune thrombocytopenic purpura (ITP), Rheumatoid Arthritis, interstitial nephritis, thyroiditis, and systemic Lupus erythematosus. If psoriasis appears, the medication may need to be discontinued.

Blood glucose (sugar): Pegasys (Peginterferon-alfa-2a) can cause low or high blood sugar. People with Diabetes should discuss with their doctor how Pegasys (Peginterferon-alfa-2a) may affect their medical condition, how their medical condition may affect the dosing and effectiveness of Pegasys (Peginterferon-alfa-2a), and whether any special monitoring is needed. If you experience high blood sugar (increased thirst, hunger, weakness, drowsiness, blurred vision, weight loss) or low blood sugar (headache, hunger, weakness, irritability, trouble concentrating) while taking Pegasys (Peginterferon-alfa-2a), contact your doctor.

Blood problems: Pegasys (Peginterferon-alfa-2a) may suppress bone marrow function and cause blood problems such as low platelet counts, low white blood cell counts, and anemia. Your doctor will monitor you for these problems with blood tests. If you experience persistent fever and chills, tiredness, shortness of breath, or easy bruising or bleeding, contact your doctor.

Colon disorders: Pegasys (Peginterferon-alfa-2a) may cause certain types of colitis. Report any stomach or abdominal pain, bloody diarrhea, or fever to your doctor immediately.

Depression and other psychiatric conditions: Pegasys (Peginterferon-alfa-2a) can cause depression and other psychiatric conditions. People with psychiatric conditions should be closely monitored by their doctor while using Pegasys (Peginterferon-alfa-2a), as it may worsen these conditions.

If you experience symptoms of depression such as poor concentration, changes in weight, changes in sleep, decreased interest in activities, or notice them in a family member who is taking Pegasys (Peginterferon-alfa-2a), contact your doctor as soon as possible.

Dizziness/reduced alertness: Peginterferon alfa-2a may affect the mental or physical abilities needed to drive or operate machinery. Avoid driving, operating machinery, or performing other hazardous tasks until you have determined how Pegasys (Peginterferon-alfa-2a) affects you.

Eye disorders: Certain eye disorders have been observed in people using Pegasys (Peginterferon-alfa-2a). If you experience any changes in vision while taking Pegasys (Peginterferon-alfa-2a), contact your doctor.

Flu-like symptoms: Pegasys (Peginterferon-alfa-2a) may cause a flu-like reaction with aching muscles, fever, chills, and headache. Your doctor may prescribe Acetaminophen before each dose of Pegasys (Peginterferon-alfa-2a) and as needed to help reduce these symptoms.

Fluids: Pegasys (Peginterferon-alfa-2a) may cause dehydration. People taking Pegasys (Peginterferon-alfa-2a) should drink adequate fluids, especially on hot days or when exercising.

Heart disease: Pegasys (Peginterferon-alfa-2a), as well as others like it, can cause heart problems such as high blood pressure, chest pain, heart attack, abnormal heart rhythms, and heart failure. If you have had a heart attack, heart failure, or changes in heart rhythm (Arrhythmias), discuss with your doctor how Pegasys (Peginterferon-alfa-2a) may affect your medical condition, how your medical condition may affect the dosing and effectiveness of Pegasys (Peginterferon-alfa-2a), and whether any special monitoring is needed. People with severe, unstable, or uncontrolled heart disease should not use Pegasys (Peginterferon-alfa-2a).

Kidney Disease: People with kidney disease should discuss with their doctor how Pegasys (Peginterferon-alfa-2a) may affect their medical condition and whether any special monitoring is needed. People with reduced kidney function may require a lower dose.

Liver function: People who are taking Pegasys (Peginterferon-alfa-2a) will need frequent checkups to test their liver function. People with reduced liver function may require a lower dose of the medication or may need to stop taking it.

Lung disorders: Certain lung disorders may occur in people using Pegasys (Peginterferon-alfa-2a), causing breathing difficulty. These conditions can be fatal. If you experience fever, cough, or shortness of breath, contact your doctor as soon as possible.

Pancreatitis: Pegasys (Peginterferon-alfa-2a) may cause pancreatitis, which may be fatal. If you develop symptoms of pancreatitis (e.g., severe abdominal pain with or without vomiting), get immediate medical attention.

Stroke: Pegasys (Peginterferon-alfa-2a) has been associated with strokes. If you experience symptoms of a stroke (e.g., sudden and severe headache, sudden weakness or numbness in the arms or legs, sudden vision changes, sudden dizziness) while taking Pegasys (Peginterferon-alfa-2a), get immediate medical attention.

Thyroid disorders: Pegasys (Peginterferon-alfa-2a) can cause or worsen Hypothyroidism (low thyroid) or Hyperthyroidism (high thyroid). People with thyroid conditions should discuss with their doctor how Pegasys (Peginterferon-alfa-2a) may affect their medical condition, how their medical condition may affect the dosing and effectiveness of Pegasys (Peginterferon-alfa-2a), and whether any special monitoring is needed.

Transplants: The safety and effectiveness of using Pegasys (Peginterferon-alfa-2a) have not been established for people who have had a liver or other organ transplant.

Pregnancy: Pegasys (Peginterferon-alfa-2a) should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking Pegasys (Peginterferon-alfa-2a), contact your doctor immediately. Women who may become pregnant should use an effective method of birth control while using peginterferon alfa-2a.

Breast-feeding: It is not known if peginterferon alfa-2a passes into breast milk. If you are a breast-feeding mother and are taking Pegasys (Peginterferon-alfa-2a), it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children and adolescents: The safety and effectiveness of using Pegasys (Peginterferon-alfa-2a) have not been established for children under the age of 18. Pegasys (Peginterferon-alfa-2a) is not recommended for use by newborns or infants because peginterferon alfa-2a contains benzyl alcohol and may be harmful.